The present invention relates to a solid polymer electrolyte fuel cell which prevents the lowering of a cell voltage by eliminating the crossover of a reactant gas and a liquid and enables the employment of a hydrocarbon ion exchange membrane which is inexpensive and has a low resistance.
A solid polymer electrolyte fuel cell attracts more attention as an electronic power source of an electric automobile and a space craft compared with a phosphoric acid fuel cell because it is compact and may take out high current density.
The electrode structure of a conventional fuel cell is ordinarily a five-layered sandwich structure which consists of a cathode current collector, a cathode, a solid polymer electrolyte (ion exchange membrane), an anode and an anode current collector. A hydrogen gas and an oxygen gas are supplied to and diffuse into an anode and a cathode, respectively, and as result an anode potential and a cathode potential deviate from a normal oxidation reduction potential so as to lower a cell voltage if the thickness of the membrane is thin. The lowering of the cell voltage due to the crossover of the gases has been conventionally prevented by depressing the permeation of the gases in the membrane by means of making the membrane thickness more than a certain value (about 100 .mu.m).
However, inconveniently, the resistance increases and the current density obtained decreases when the membrane thickness is thick.
A perfluorocarbon membrane of a sulfonic acid type or a carboxylic acid type which is chemically stable is employed as the ion exchange membrane of a fuel cell. This is because of the deterioration of the cheap hydrocarbon ion exchange membrane due to oxidative decomposition caused by a radical generated in a cathode reaction. Since the chemically stable perfluorocarbon type ion exchange membrane possesses a large molecular weight, an equivalent weight (EW) per unit functional group is large so that ionic conductivity decreases and a resistance increases. In the other words, the conventional fuel cell has the drawbacks that the ionic conductivity is large and the lowering of the resistance by employing the cheap hydrocarbon ion exchange membrane cannot be attained as well as the membrane thickness cannot be made thin to lower the resistance in the case of employing the perfluorocarbon type membranes.